1. Field of the Invention
The present invention relates to an organic electroluminescence (EL) display device, and more particularly to a technique for improving the reliability of a sealing film that covers an upper portion of an organic light emitting element.
2. Description of the Prior Art(s)
FIG. 12 is a schematic partially cross-sectional view of a display area of a related art organic EL display device 2, which illustrates a cross section along a horizontal direction of a display area. The organic EL display device 2 has a structure in which a TFT substrate 4 and an counter substrate 6 are bounded with each other through a filler layer 8 sandwiched therebetween. The TFT substrate 4 is formed, for example, in such a manner that a circuit part 12, an OLED part 14, and a sealing layer 16 are laminated on a glass substrate 10. The counter substrate 6 is formed, for example, in such a manner that a color filter 22 is laminated on a glass substrate 20.
An organic light emitting diode (OLED) which is an organic light emitting element is formed for each pixel in the OLED part 14 of the TFT substrate 4, and a bank is formed in a boundary between the adjacent pixels as a partition between those pixels. The OLED includes a lower electrode 30, an organic layer 32, and an upper electrode 34. The lower electrode 30 and the upper electrode 34 configure an anode electrode (anode) and a cathode electrode (cathode) of the OLED, respectively. The upper electrode 34 is formed to be shared with pixels in an overall display area, and applied with a common voltage from a drive part. On the other hand, the lower electrode 30 is formed for each of the pixels. A bank is formed between the respective adjacent pixels with an insulating layer, and electrically isolates the respective lower electrodes 30 from each other.
The sealing layer 16 is laminated on the OLED part 14. In response to a fact that the characteristic of the OLED is deteriorated by moisture, the sealing layer 16 has a moisture-proof function for protecting the OLED from moisture, for example, contained in the filler layer 8. The sealing layer 16 is formed in such a manner that a first barrier layer 40, which is an inorganic passivation film made of silicon nitride (SiN), a flattening layer 42 made of acrylic resin, and a second barrier layer 44, which is the same inorganic passivation film as that of the first barrier layer 40, are laminated in the stated order (refer to Japanese Patent No. 4303591 and JP 2007-156058 A). In this configuration, the first barrier layer 40 and the second barrier layer 44 function as a sealing film for blocking the transmission of a material that deteriorates the OLED such as moisture.
On the other hand, the flattening layer 42 flattens the irregularity of a surface of the first barrier layer 40. As the flattening layer 42, acrylic monomer is adhered onto the surface of the first barrier layer 40 by vapor deposition or the like. The acrylic monomer has fluidity, is aggregated on an irregular portion by surface tension, and makes the undulation of the irregular portion gentle. With this property, inner corners 50 at steps of pixel edges which are caused by the banks are filled with the acrylic monomer for smoothing. The acrylic monomer is polymerized by the irradiation of ultraviolet rays into acrylic resin in a state where the irregularity is thus smoothed. With the provision of the flattening layer 42, the second barrier layer 44 is optimally formed.